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Physics Astrophysics Cosmology and Nongalactic Astrophysics

astro-ph.CO Watch Cosmology and Nongalactic Astrophysics

Tuesday 6 October

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Universal Relations Meet Causality: Bounding the Dynamical Love Number of Neutron Stars

Alex Kehagias and Antonio Riotto

The frequency-dependent tidal response of a neutron star is constrained by causality, reality and passivity, which turn a suitably rescaled response into a holomorphic self-map of the upper complex frequency half-plane after some suitable conditions. The Schwarz–Pick theorem then bounds the leading dynamical correction to the tidal deformability from above. In this work we confront this bound with the most recent calculations of the dynamical tidal response in the literature which have also shown that the static tidal deformability and its correction at second order in frequency are tightly correlated. We find that the bound is saturated to within a few per cent, a quantitative confirmation of f-mode dominance in the relativistic regime. The combination of the static deformability with an independent determination of the f-mode frequency thus may provide an equation-of-state-independent upper limit on the dynamical tide.
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Cosmology and Nongalactic Astrophysics

The impact of feedback and cosmology on Cosmic Infrared Background cross-correlations

Sara Maleubre, David Alonso, Reggie Dunsdon et al. (+3 more)

We study the evolution and clustering properties of the star formation rate density (SFR) $\rho_{\rm SFR}$ in the FLAMINGO suite of hydrodynamical simulations, with the aim of exploring the possibility of constraining AGN and stellar feedback prescription, as well as the effect of cosmology, using cross-correlations between the Cosmic Infrared Background (CIB) and other tracers of the large-scale structure. Specifically, we consider tomographic measurements of the bias-weighted SFR-density $\langle b\rho_{\rm SFR}\rangle$, as well as cross-correlations between the CIB and cosmic shear as a probe of the $\rho_{\rm SFR}$-matter correlation. Most of the FLAMINGO models calibrated against the $z=0$ galaxy stellar mass function (SMF) yield similar predictions for the distribution and clustering of star-forming systems, and thus it is difficult to derive clean conclusions regarding the impact of AGN feedback or cosmology on CIB statistics. However, we show that current measurements of $\langle b\rho_{\rm SFR}\rangle$, as well as CIB-shear cross-correlations clearly disfavour models with strong stellar feedback, as well as simulations with strong kinetic (jet-driven) AGN feedback, even under the fiducial SMF calibration. This study demonstrates the potential of CIB cross-correlations to study aspects of the physics of star and galaxy formation in a cosmological setting.
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All authors Sara Maleubre, David Alonso, Reggie Dunsdon, Adrien La Posta, Amy Wayland, Joop Schaye

Cosmology and Nongalactic Astrophysics

ApPolLO: Apertif counterparts of Polarised LOFAR sources

A. Berger, B. Adebahr, H. Dénes et al. (+1 more)

Knowledge of the structure and evolution of cosmic magnetic fields is indispensable to understand how primordial magnetic fields were generated and amplified during the lifetime of the Universe. Polarisation studies over significant redshift ranges are an important tool in understanding cosmic magnetic fields. We aim to understand the structure and evolution of cosmic magnetic fields, utilising the polarised spectra and depolarisation characteristics of (background) radio sources. Using radio polarisation data at two different frequencies from the LOFAR Rotation Measure (RM) grid catalogue at 144\,MHz and new Apertif data at 1.4\,GHz, we investigate the source statistics of a common sample of polarised sources, deriving the depolarisation ratio between these two frequencies. We utilise this to disentangle depolarising effects local to the source from those along the line of sight. We compile a catalogue of 598 polarised radio components, most of which are located in low-density environments. Fractional polarisation decrease for both wavelengths with redshift. We attributed the main depolarisation at 1.4\,GHz to effects occurring close to the sources, while the depolarisation measured at 144\,MHz is most likely generated by cosmic filaments along the line-of-sight. We were able to get a first redshift dependent upper limit estimate of the RM dispersion in cosmic web filaments.
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All authors A. Berger, B. Adebahr, H. Dénes, R.-J. Dettmar

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Gravitational Waves and Nambu-Goldstone Bosons from Infrared-Finite Cosmic Strings

Hajime Fukuda, Shuailiang Ge and Keisuke Harigaya

Skyrmion lines and semi-local strings are examples of infrared-finite cosmic strings that arise in theories with spontaneously broken global symmetries. Unlike global $U(1)$ strings, they do not support the long-range Nambu-Goldstone boson (NGB) profile responsible for a logarithmically infrared-divergent string tension. We argue that NGB emission from their low-frequency oscillations is strongly suppressed. Consequently, their gravitational-wave signals may be comparable to those from local strings.
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Cosmology and Nongalactic Astrophysics

Evolution of neutrino distributions under repeated electron scattering

Jens Chluba, Bryce Cyr, Michiru Uwabo-Niibo et al. (+1 more)

We study the energy redistribution of neutrinos by repeated elastic scattering with an isotropic thermal bath of free electrons. Starting from the relevant Boltzmann collision integral, we formulate the evolution equations in terms of the neutrino–electron redistribution kernel derived in our companion work. The scattering kernel formulation retains recoil, relativistic kinematics and Pauli blocking, while reducing the calculation to a one-dimensional integral in the outgoing neutrino energy. To gain a better analytic understanding, we derive the corresponding Fokker–Planck (FP) limit of the collision operator in two independent ways and contrast it with the Kompaneets equation for photons. This shows that the different energy dependence of the weak cross section changes the drift and diffusion operators which causes the high-energy part of a neutrino distribution to evolve much faster than its low-energy part. We discuss the fermionic analogues of temperature-, chemical-potential- and $y$-type spectral distortions, and give approximate analytic solutions to the FP equation in several limiting cases. We also derive the analytic expressions for the relativistic scattering operator when Doppler terms dominate, allowing us to compute the relativistic Sunyaev-Zeldovich equivalent for neutrinos in the inefficient scattering limit. We compare these expressions to the full numerical result based on the detailed collision term. Finally, we set up conservative numerical schemes for both the FP equation and the scattering kernel, generalizing previous codes developed for studying the repeated Compton scattering of photons by relativistic electrons. Controlled line-injection experiments then illustrate when the diffusion approximation is accurate and where the non-locality of the redistribution kernel remains essential.
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All authors Jens Chluba, Bryce Cyr, Michiru Uwabo-Niibo, Masahide Yamaguchi

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Flavor decoherence and washout timing in nonthermal leptogenesis after inflation

Boliang Yu and Ruixin Zhou

We investigate why changing the heavy-neutrino mass hierarchy can reverse the baryon asymmetry in nonthermal leptogenesis after hilltop inflation. Along the mass trajectory studied here, lowering the mass of the lighter state, \(N_1\), reverses the final asymmetry while leaving the dominant injection from \(N_2\) decays nearly unchanged. The mass change primarily delays \(N_1\) washout relative to electron–muon flavor decoherence; at fixed source and background, translating the washout history while preserving its shape and integrated strength reproduces more than 99% of the yield changes from the nonthermal \(N_2\) source at two physical target masses. Decomposing the \(N_2\) CP source shows that the projector-aligned component remains positive under both washout histories, whereas the initially trace-free component reverses its propagated contribution and accounts for about 99.7% of the timing contrast in the fixed-source comparison. Rapid damping of \(e\mu\) flavor coherence largely removes this contrast, while rapid chemical equilibration does not. Later washout therefore acts on a more decohered flavor state, reducing the positive \(e\mu\) contribution and allowing negative diagonal contributions to determine the final sign. At a mass recomputed to reproduce the observed baryon yield, a 10% increase of the muon collision operator reverses the sign in a fixed-input sensitivity test.
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Cosmology and Nongalactic Astrophysics

Probing beyond the Cosmic Horizon

Tarun Souradeep

There are reasons to believe that the region of uniform curvature that we observe within our horizon is perhaps a tiny patch, much smaller than the length scales of inhomogeneity and global connectivity of an extremely complicated manifold. However, the recent supernova (SN) results suggest that the horizon scale could be comparable to or even much larger than curvature radius. Non trivial global structure too tends to be of the order of the local curvature scale. Probing (slightly) beyond the cosmic horizon can potentially reveal nontrivial global structure lurking around or just beyond the horizon scale. The cosmic microwave background (CMB) anisotropy is a sensitive probe of the universe on length scales up to and somewhats beyond the horizon scale and is perhaps poised to detect or put interesting limits on nontrivial features the global structure. This point is exemplified by high CMB anisotropy signal of the Elliptical topology in a large fraction of the revised parameter space of the closed FRW universe (spherical geometry) currently preferred by SN observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Axion Pyramid

Chan-Gyung Park, Dahee Lee, Hyerim Noh et al. (+1 more)

A pronounced pyramid-shaped enhancement in the axion density power spectrum induced by the QCD phase transition is identified. The enhancement occurs near the horizon scale at the transition, with a characteristic comoving length scale comparable to the size of the Solar System, and amplifies the axion density perturbation by factors exceeding $3.5 \times 10^{13}$ relative to the CDM case. Under the hilltop initial condition, coupling to radiation triggers this enhancement. The initial condition is related to the axion mass, suggesting that observation of the axion pyramid in cosmology may constrain the QCD axion mass.
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All authors Chan-Gyung Park, Dahee Lee, Hyerim Noh, Jai-chan Hwang

Cosmology and Nongalactic Astrophysics

Third-order scalar induced gravitational waves during a matter-dominated era: secular growth and implications for primordial black hole domination

Jing-Zhi Zhou

We investigate scalar induced gravitational waves (SIGWs) at third-order during a matter-dominated (MD) era. We classify the sources into four parts—built from three first-order scalars, and from a first-order scalar times the second-order tensor, vector, and scalar perturbations—and obtain all four kernel functions analytically in closed form. Unlike their radiation-dominated counterparts, the MD kernel functions grow secularly, translating into a rapid growth of the spectrum, $\Omega^{(3)}_{\mathrm{GW}}\propto x^{6}$ versus $\Omega^{(2)}_{\mathrm{GW}}\propto x^{2}$ at $x\equiv k\eta\gg1$. We derive the third-order power spectrum as a five-fold integral for a general primordial spectrum, and evaluate it numerically for a monochromatic one, where all contributions from the second-order vector source vanish identically. As an application, we consider the early MD era driven by primordial black holes (PBHs) before their evaporation. Requiring that the induced gravitational waves do not backreact on the cosmological perturbations, $\int\mathrm{d}\ln k\, \Omega^{\mathrm{tot}}_{\mathrm{GW}}<1$ then bounds the initial PBH abundance as $\Omega_{\mathrm{PBH},f}\lesssim4.6\times10^{-7}\, (m_{\mathrm{PBH}}/10^{7}\,\mathrm{g})^{-0.48}$, about three orders of magnitude stronger than the second-order-only bound. Our results indicate that higher-order SIGWs inevitably become nonperturbative during a sufficiently long MD era, with important implications for scenarios involving an early matter domination.
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Cosmology and Nongalactic Astrophysics

Fast and accurate differentiable code of the galaxy power spectrum based on Eulerian and Lagrangian one-loop perturbation theories

Yosuke Kobayashi and Kazuyuki Akitsu

This paper presents a JAX-Python implementation of the galaxy power spectrum up to one-loop order in the effective field theory of large-scale structure, based on both the Eulerian and Lagrangian perturbation theories. The code uses JAX to enable automatic differentiation with respect to parameters such as cosmology, galaxy bias, or counterterm coefficients. This facilitates applications such as parameter inference using the gradient of the posterior, e.g., Hamiltonian Monte Carlo sampling. The code can compute both the EPT and LPT power spectra in a few milliseconds on a GPU, after just-in-time compilation. We also identify the various sources of numerical errors associated with discretization, and design the numerical implementation to minimize them, achieving relative errors of order $0.01\%$ at scales $k \lesssim 1\, h\, \mathrm{Mpc}^{-1}$, compared with brute-force numerical integration. Notably, this is the first auto-differentiable implementation of the one-loop galaxy power spectrum based on LPT. The natural resummation of the long-wavelength displacements in LPT further makes the code well suited for applications involving features in the power spectrum beyond the standard BAO feature, including primordial features. Our code, elf, is publicly available.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Chaotic accretion can (still) explain early supermassive black hole growth

Kastytis Zubovas and Matas Tartėnas

The origin of supermassive black holes (SMBHs) is still debated, with hypotheses ranging from massive seeds to super-Eddington growth to chaotic accretion. Recent discoveries of very high redshift SMBHs constrain their possible origin and growth scenarios. We investigate whether the chaotic accretion scenario can explain the most extreme high-redshift SMBH masses. We predicted the exponential growth timescale of black holes accreting chaotically in a slowly-spinning dark matter halo, in which uncorrelated gas inflows maintain a low spin and hence a low radiative efficiency. We compared this prediction against the growth timescales and seed masses implied by a compilation of all known SMBH mass estimates at $z>7$ and against the feeding and feedback conditions expected in such haloes. We found that in the period $7.6 < z < 10.6$, the most massive SMBHs likely grew very efficiently, with an exponential growth timescale $\tau \sim 32$~Myr, which is consistent with chaotic accretion predictions provided that growth was almost continuous. All high-redshift SMBHs with virial mass estimates could have grown from seeds with $M_{\rm seed} \lesssim 100 \, \msun$. We describe the evolution of the mass reservoir feeding such a black hole, suggesting that wind-driven feedback eventually removes most of the gas and changes the growth mode of black holes at $z \sim 7.5$. We make several predictions regarding the spins, host-galaxy correlations, and observable counterparts of high-redshift SMBHs that distinguish our model from its alternatives. These predictions will be testable in the near future. Chaotic accretion from stellar-mass seeds remains a viable origin for the earliest known SMBHs, without invoking massive seeds or super-Eddington growth.
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Cosmology and Nongalactic Astrophysics

Stochastic Bubble Completion in de Sitter Space: Power Spectrum, Bispectrum, and Infrared Moment Hierarchies

Hyukjung Kim, Alp Kagan Ozmen and Heeseung Zoe

Stochastic bubble nucleation makes the local completion time of a first-order phase transition a random spatial field. We study its power spectrum and equilateral bispectrum in Minkowski and de Sitter backgrounds, with particular emphasis on the infrared consequences of a finite transition duration. In an eternally extended de Sitter history, rare bubbles nucleated in the remote past generate an ancient-bubble tail that produces a hierarchy of infrared-sensitive spatial moments. For the two-point function, the first finite-$k$ correction becomes tail sensitive at $H/\beta=1/5$, while the leading moment becomes singular at $H/\beta=1/3$. The corresponding three-point thresholds are $H/\beta=1/8$ and $1/6$, showing that the bispectrum is more infrared sensitive than the power spectrum. For any finite starting time, however, the ancient-bubble tail is cut off, all spatial moments remain finite, and the strict infrared spectra recover the analytic white-noise limits ${\cal P}_\tau\propto k^3$ and ${\cal B}^{\rm eq}_\tau\propto k^6$. The eternal-background thresholds instead control the duration dependence of the moment coefficients and the crossover into an intermediate tail-sensitive regime, in agreement with our numerical calculations. We further show that temporal localization of the nucleation history provides a smooth regulator of the ancient-bubble tail and restores the same analytic infrared limits. These results establish a general first-arrival framework for completion-time fluctuations and clarify how de Sitter expansion can generate distinct power-spectrum and bispectrum infrared hierarchies relevant to curvature perturbations and non-Gaussianity.
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Monday 5 October

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Spectator Dark Matter and the Higgs Portal

Stephen E. Henrich, Yann Mambrini and Keith A. Olive

Light scalar spectators generically acquire large stochastic fluctuations during inflation, which can lead to a catastrophic overproduction of dark matter if the resulting primordial condensate survives until late times. We show that this inflationary memory can be sufficiently suppressed by an extremely feeble Higgs portal interaction with sub-freeze-in couplings ($10^{-28} \lesssim \lambda_{HS} \lesssim 10^{-9}$). The Higgs portal induces both a radiative self-interaction for the spectator as well as a thermal mass, both of which can lead to early onset of oscillations and efficient redshifting of the condensate's energy density without thermalizing the spectator or destroying the condensate. The Higgs portal also alters the stochastic equilibrium distribution of the spectator fluctuations, leading to a suppression of the field variance relative to an isolated spectator. We include a detailed treatment of the possibility that inflation may not have lasted sufficiently long for the spectator to reach its equilibrium distribution of fluctuations, finding the major constraint on such a scenario to come from isocurvature, which requires $N \gtrsim10^{10}$ e-folds. We also consider the addition of a non-minimal gravitational coupling, which extends the parameter space significantly. This model generally favors sub-GeV light dark matter ($0.1 \text{ eV} \lesssim m_S \lesssim 10 \text{ GeV}$) and in the absence of non-minimal gravity it also favors low reheating temperatures. While this mechanism can supply the entire relic abundance with sub-freeze-in portal couplings, it also naturally provides a suppressed initial condition for standard Higgs portal freeze-in.
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Cosmology and Nongalactic Astrophysics

Lensing in the Blue IV: The First Weak Gravitational Lensing Maps from the Stratosphere

Sayan Saha, Maya Amit, Jacqueline E. McCleary et al. (+42 more)

The Super-Pressure Balloon-borne Imaging Telescope (SuperBIT) completed its science flight in April 2023, obtaining imaging data for 30 galaxy clusters. In this work, we present the first weak-lensing convergence maps from these observations, using six clusters selected from the 30 targets. We construct background-galaxy catalogs using SuperBIT's three-band photometry and a color-color-based method to separate foreground and background galaxies, and use the calibrated galaxy shapes presented in Lensing in the Blue III to reconstruct the weak-lensing convergence field using Kaiser-Squires inversion. We compare the convergence signal-to-noise maps for the six clusters with independent tracers, including X-ray emission and red-sequence cluster-member number-density maps. These results demonstrate the first successful weak-lensing mass mapping with imaging from a sub-orbital astronomical observatory.
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All authors Sayan Saha, Maya Amit, Jacqueline E. McCleary, Georgios N. Vassilakis, Emaad Paracha, Giulia Cerini, Spencer W. Everett, Leila Ohashi, Eric M. Huff, Gavin Leroy, Leo W.H. Fung, Richard Massey, Steven J. Benton, William C. Jones, Thuy Vy T. Luu, Ajay S. Gill, Mohamed M. Shaaban, Philippe Voyer, Adam Field, Adam Aoua, Anthony M. Brown, Paul Clark, Matthew Craigie, Christopher J. Damaren, Tim Eifler, David Harvey, Eric Habjan, John W. Hartley, Bradley Holder, Mathilde Jauzac, David Lagattuta, Jason S.-Y. Leung, Lun Li, Johanna M. Nagy, C. Barth Netterfield, Susan F. Redmond, Jason D. Rhodes, Andrew Robertson, L. Javier Romualdez, Jürgen Schmoll, Ellen Sirks, Sut Ieng Tam, Karuna Tarafdar, André Z. Vitorelli, Alfredo Zenteno

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Hierarchical Black Hole Mergers at High Redshift: Predictions for LISA and LGWA from SEEDZ

Daxal H. Mehta, Lewis R. Prole, John A. Regan et al. (+13 more)

We investigate the hierarchical assembly of black holes (BHs) in the early Universe using the next-generation SEEDZ cosmological zoom-in simulations. Our suite follows two independent regions (Rarepeak and Normal1) evolved with three BH feedback prescriptions: no feedback (NoFB), weak feedback (WeakFB), and standard thermal isotropic feedback (FidBH). Focusing on BH mergers at $z \geq 10$, we explore merger-driven BH growth and detectability with next-generation gravitational-wave observatories. We find that stronger AGN feedback models dramatically suppress hierarchical BH assembly compared to weaker feedback implementations. In the NoFB simulations, BHs frequently undergo repeated mergers, with some experiencing more than 50 merger events within a few hundred Myr and gaining over $10^8,\mathrm{M_{\odot}}$ through mergers alone. In contrast, BHs in the FidBH simulations rarely undergo more than three mergers. NoFB therefore represents an upper limit to BH merger-driven growth beyond what is expected in the Universe. The suppression of BH mergers in the FidBH case is not driven by differences in galaxy assembly, BH occupation fractions, or BH seed abundances, which remain broadly similar across the simulation suites. Instead, feedback disrupts the dense gas surrounding newly formed BH seeds, suppressing their early accretion-driven growth and preventing them from entering runaway hierarchical merger pathways. Our results demonstrate that early-Universe feedback prescriptions strongly influence hierarchical BH growth through both mergers and accretion, producing distinct high-redshift merger populations. Coupled with seeding choices and other BH subgrid prescriptions, this introduces multiple degeneracies that will need to be broken in advance of LISA and other next-generation GW facilities.
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All authors Daxal H. Mehta, Lewis R. Prole, John A. Regan, Rüdiger Pakmor, Sophie Koudmani, Ricarda S. Beckmann, Michael Tremmel, John H. Wise, Martin A. Bourne, Ralf S. Klessen, Simon C. O. Glover, Martin G. Haehnelt, John Brennan, Pelle Van De Bor, Debora Sijacki, Paul C. Clark

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Coherent versus incoherent amplification: from parametric resonance to the kinetic regime in stimulated axion decay

Clemente Smarra and Elisa Todarello

Although the spontaneous decay of axions into two photons is extremely slow on cosmological timescales, it can be strongly enhanced in environments with large bosonic occupation numbers. From a classical field perspective, stimulated axion decay is described by modified Maxwell equations. For a coherent axion background, these equations exhibit a parametric resonance characterized by a photon growth exponent $s\propto g_{a\gamma}$. By contrast, a standard kinetic description, for instance based on Boltzmann equations, involves the squared matrix element of the decay process and therefore would naturally predict a characteristic rate scaling as $s\propto g_{a\gamma}^2$. In this work, we show that these apparently different behaviors originate from the coherence properties of the axion field. Starting from an axion field with a finite momentum dispersion, we show how dephasing among its momentum modes modifies the photon instability and derive an effective evolution equation in which this effect is encoded in a kernel. For a continuous Maxwell-Boltzmann distribution of axion velocities, we obtain an implicit expression for the photon growth exponent that reproduces the two asymptotic regimes and provides an approximate description of the crossover. When amplification develops on scales shorter than the axion coherence length, the parametric resonance scaling $s\propto g_{a\gamma}$ is recovered, whereas in the opposite limit an effectively kinetic behavior with $s\propto g_{a\gamma}^2$ emerges. Although the detailed form of the crossover depends on the axion momentum distribution, we expect the asymptotic scaling with $g_{a\gamma}$ to be largely insensitive to the specific distribution assumed.
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Cosmology and Nongalactic Astrophysics

And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time

Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich et al. (+2 more)

Observations of the local Universe show that, except in the most massive galaxy clusters, the baryon fraction within halos falls below the cosmic mean. This deficit can be characterized using the previously established closure radius, the halocentric distance within which the enclosed baryon fraction reaches the cosmic value. Using the TNG, EAGLE and SIMBA simulations, we examine how, when, and on what scales the baryonic and dark matter distributions diverge. At z=0 less than 30% of cosmic baryons reside within galaxy-hosting halos, compared with ~45% of the dark matter, leaving over 70% of all baryons in the IGM. Building on the closure radius, we introduce three further characteristic scales: the compensation radius, closure envelope, and compensation envelope. The compensation radius marks where the enclosed total mass recovers its gravity-only value, and today it typically lies inside the closure radius in all three models. The closure and compensation envelopes are the largest median radii across halo mass. Galaxy groups provide the largest contribution per dex of halo mass to IGM enrichment with halo-associated baryons and redistribute baryons over the largest distances. They set the closure envelope, which reaches ~2-6.5 Mpc at z=0, depending on the model. The closure radius usually increases with cosmic time at fixed halo mass. Tracking individual halos, we find open baryon cycles with substantial redistribution beyond halo boundaries across all halo masses, while even the progenitors of today's most massive clusters fall below the cosmic baryon fraction. The compensation envelope grows toward low redshift, reaching ~1.5-5.5 Mpc at z=0. Across cosmic time, it coincides with the scale on which the matter power spectrum recovers its gravity-only form, establishing a direct link between the spatial extent of baryon redistribution and the impact of feedback on large-scale structure.
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All authors Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich, Cristiano Porciani, Dominique Eckert

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

EMIR confirmation of the high-z Ly{\alpha} blob SHARDS20018464

S.Zarattini, F. Garzón and C. Muñoz-Tuñón

A spectroscopic follow-up of the Ly$\alpha$ blob SHARDS20018464 was performed using the infrared spectrograph EMIR (Espectrógrafo Multiobjeto Infra-Rojo) at the 10.4 m GTC telescope, equipped with its newly upgraded H2RG focal plane array detector. We observed the blob in the Ks band, which corresponds, at the photometric redshift of $z=3.49$ presented in the literature, to the rest-frame visible part of the spectrum. Thanks to the sensitivity of EMIR, we were able to identify the [OIII] emission doublet at the position of the blob and the companion galaxy. The flux of the detected lines is of the order of $10^{-17}$ erg s$^{-1}$ cm$^{-2}$, obtained with 4-hour exposure. The mean redshift derived by analysing the two lines individually is $z=3.59\pm0.01$, slightly higher than the photometric one, although in agreement within the uncertainties. We also estimated the flux of the two lines and their ratio, which was found to be $R = 2.92$, very close to the theoretical prediction of 2.98. This is a strong analytical confirmation that the observed emissions correspond to the [OIII] doublet. Within uncertainties, the redshift of the blob confirms the photometric one reported in the literature, as well as the physical properties inferred for it. Its remarkably small size (5-8 kpc vs. $\sim 100$ kpc for typical samples) and its position aside the companion galaxy also confirm the previously-proposed idea that this object could be the first of a new class of compact Ly$\alpha$ emitters. Moreover, the data support the scenario of photo-ionisation due to a cluster of young and massive stars.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Lunar radio emission from dark photon dark matter

Ariel Arza

The dielectric surface of the Moon provides an efficient interface for the conversion of dark matter dark photons into radio waves. This work explores a novel detection strategy that aims to capture this radio emission using standard radio telescope antennas. Detailed sensitivity projections are presented that demonstrate the power of this technique. It is found that both current and future radio observatories, including large arrays such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the Square Kilometer Array (SKA), as well as large single dishes like the Five-hundred-meter Aperture Spherical Telescope (FAST) and the Green Bank Telescope (GBT), can explore a substantial and previously inaccessible parameter space for these dark matter candidates.
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Cosmology and Nongalactic Astrophysics

Testing Refracted Gravity with the kinematics of stacked galaxy clusters

Dario Primignani, Lorenzo Pizzuti, Antonaldo Diaferio et al. (+1 more)

We test Refracted Gravity (RG), a phenomenological modified gravity model that modifies the Poisson equation by introducing an effective gravitational permittivity $\epsilon(\rho_{\rm bar})$ which depends on the baryonic matter density $\rho_{\rm bar}$ and mimics the behaviour of dark matter in cosmic structures. We perform a kinematical analysis of member galaxies for a sample of 74 galaxy clusters, compiled from the Cluster Infall Regions in the Sloan Digital Sky Survey (CIRS). We stack the clusters in three bins of increasing velocity dispersion to mitigate the effects of systematic errors induced by deviations from dynamical equilibrium and from the assumption of spherical symmetry. By means of the MG-MAMPOSSt code, we reconstruct the gravitational potential in RG and infer the model parameters jointly with the gas and stellar mass-profile parameters, adopting broad, physically informed priors on the baryonic components. The estimates of the main parameter in Refracted Gravity, the vacuum permittivity $\epsilon_0$, range from $0.04$ to $0.37$, across the three main stacks, depending on the model adopted for the hot gas component. The constraints are mutually compatible within the quoted uncertainties and overlap with previous cluster-scale estimates. The agreement becomes less sensitive to gas parametrisation when selecting the less-disturbed clusters for building the stacks. These results characterize the sensitivity of cluster-scale RG constraints to baryonic modelling and sample selection
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All authors Dario Primignani, Lorenzo Pizzuti, Antonaldo Diaferio, Valeria Broccolato

Cosmology and Nongalactic Astrophysics

AI-assisted super-resolution cosmological simulations V: Cosmology-aware super-resolution

Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft et al. (+2 more)

We present a cosmology-aware generative model for super-resolution (SR) of cosmological $N$-body simulations in particle phase space. The model jointly generates displacements and velocities, conditioning a generative adversarial network (GAN) based generator and discriminator on evolved low-resolution (LR) fields and five $\Lambda$CDM parameters $(\Omega_m,\Omega_b,h,n_s,\sigma_8)$. We train a single model on 100 matched low-high resolution pairs from the Quijote Latin-hypercube suite at $z = 0$, mapping $512^3$ to $1024^3$ particles in $1\,h^{-1}\,\mathrm{Gpc}$ boxes. On ten cosmologies excluded from SR training, the model reproduces the broad matter distribution and the cosmological variation of clustering and halo abundances. Over $0.1<k<3\,h\,\mathrm{Mpc}^{-1}$, the mean of the per-cosmology maximum absolute power-spectrum errors is $3.6\%$, while FoF halo abundances agree with HR to within $15\%$ in the analyzed mass bins below $10^{14.8}\,h^{-1}M_\odot$. Satellite abundances and occupations retain larger, mass-dependent discrepancies. Corrections measured at one near-fiducial cosmology reduce a shared component of these systematic errors when applied to the other nine test cosmologies. A power spectrum based inference test also shows that calibration reduces the mean shifts in all parameters. These results extend our SR model across cosmologies and provide 6D phase space realizations for subsequent studies of non-linear structure and field-level cosmological inference.
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All authors Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft, Tiziana Di Matteo, Francisco Villaescusa-Navarro

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

Disentangling the assembly of the central and diffuse stellar components in galaxy clusters through dynamical friction and tidal stripping

Frazer R. Pearce, Steven P. Bamford, Garreth Martin et al. (+7 more)

In galaxy clusters, it is common to conceptually distinguish the central, brightest cluster galaxy (BCG) from the more diffuse intracluster light (ICL). So far, however, this distinction has lacked a clear physical basis, confusing both theoretical and observational studies. We address this by presenting a dynamically motivated definition of the two stellar components, evaluated using cluster zoom simulations from the Three Hundred project. We start with a motivational hindcasting approach, robustly tracing stars from the centres of 107 present-day clusters back through the merger hierarchy. We find that the majority of the final BCG stellar mass is typically contributed by the central galaxies of only 3 to 5 progenitor haloes. Most accreted galaxies contribute no stars to the BCG, instead surviving as satellites or depositing stellar material throughout the cluster. This naturally leads to a definition of the BCG stellar population as originating from the central galaxies of the most massive infalling systems. These are delivered to the cluster centre via efficient dynamical friction and subsequently undergo violent relaxation. The ICL arises from the complementary population of stars tidally stripped from the outskirts of all infalling systems. We therefore develop a forecasting method, identifying stars in the BCG and ICL via the dynamical fates of their originating stellar systems. Applying this to 261 clusters, we find the resulting components remain spatially interleaved, but occupy distinct regions of phase space. Our physically defined BCG matches conventional aperture-based selections with high completeness, while providing a direct interpretation in terms of hierarchical assembly.
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All authors Frazer R. Pearce, Steven P. Bamford, Garreth Martin, Yannick M. Bahé, Harley J. Brown, Madeline Butler, Ana Contreras-Santos, Weiguang Cui, Nina Hatch, Alexander Knebe

Cosmology and Nongalactic Astrophysics

Optimizing Color Selection for Cluster-Member Identification with SuperBIT

Leila Ohashi, Sayan Saha and Jacqueline E. McCleary

Galaxy richness maps provide a useful tracer of the stellar mass distribution in galaxy clusters, but identifying cluster members from multiband photometric data can be challenging. In this work, we investigate multiband imaging data obtained with the Super-Pressure Balloon-borne Imaging Telescope (SuperBIT) during its science flight in April 2023. Using spectroscopically identified cluster members across the SuperBIT cluster sample, we benchmark the performance of the three colors available from the three SuperBIT bands: $(u-b)$, $(b-g)$, and $(u-g)$. We quantify the performance of each color using the $1\,\sigma$ scatter of the spectroscopically identified members in color and the purity of our cluster-member identification algorithm. We find that $(b-g)$ consistently exhibits the smallest color scatter and highest purity across the sample and over the redshift range probed by SuperBIT. We therefore identify $(b-g)$ as the preferred color for red-sequence-based cluster-member identification, providing a basis for future analyses of the cluster galaxy population using SuperBIT multiband photometry.
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Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.GA

The star-forming past and quenching of brightest cluster galaxies in TNG-Cluster

Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich et al. (+2 more)

The Brightest Cluster Galaxies (BCGs) in the most massive galaxy clusters of our Universe are, at present, mostly quiescent, elliptical, and red. However, their formation histories are unclear and likely different from those of massive ellipticals in lower-mass haloes. Simulations face the challenge of simultaneously requiring large volumes to sample massive clusters and sufficient resolution to model their stellar populations. Therefore, we make use of TNG-Cluster, one of the highest-resolution cosmological simulations of galaxy clusters, which returns 352 BCGs at $z=0$ with stellar masses $M_{*, <30 \mathrm{pkpc}} = 10^{11.6-12.9} ~\mathrm{M}_\odot$ and total halo masses $M_{\mathrm{200c}} = 10^{14.3-15.4}~\mathrm{M}_\odot$. 93 per cent of the BCGs are quenched at $z=0$, whereas at redshift $z>3$ all their main progenitors were still star forming. The star-formation histories of individual BCGs are complex, including multiple (re)quenching episodes. They rejuvenate on average $2.1 \pm 1.8$ times since $z=3$. BCGs quench for the first time $9.9^{+0.9}_{-1.4} ~\mathrm{Gyr}$ ago (10th-90th percentiles; $z=1.7^{+0.5}_{-0.5}$), while the last and final quenching event occurred $7.0^{+2.8}_{-5.0} ~\mathrm{Gyr}$ ago ($z=0.8^{+0.8}_{-0.6}$). We find a large scatter in the halo, stellar, and SMBH masses at both first and last quenching, suggesting no characteristic mass at which quenching occurs. Instead, BCGs quench for the first time when the cumulative kinetic energy injected by their SMBH equals the BCG binding energy, corresponding to a delay of $2.3^{+1.2}_{-1.2} ~ \mathrm{Gyr}$ after the first SMBH kinetic energy injection. Namely, TNG-Cluster BCGs quench when they experience significant gas expulsion. Our work shows that BCGs have complex and varied star-formation histories, with multiple rejuvenation episodes, but they ultimately quench due to SMBH feedback.
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All authors Sunna Gottschewski, Joey Braspenning, Annalisa Pillepich, Katrin Lehle, Dylan Nelson

Cosmology and Nongalactic Astrophysics · Cross-listed from astro-ph.HE

Pair echo model of CTAO/LST-1 signal from GRB 221009A

Andrii Neronov, Ievgen Vovk, Teneman Keita et al. (+1 more)

Interactions of very-high energy gamma-rays during their propagation through the intergalactic medium result in a delayed secondary “pair echo” signal. Detection of such pair echo can be used for measurements of intergalactic magnetic fields (IGMF) in the voids of the Large Scale Structure of the Universe. We notice that a combination of data of LHAASO and CTAO/LST-1 telescopes on the gamma-ray burst GRB 221009A is consistent with the pair echo model. The LST-1 measurement of the source signal 1.33 days after the burst can be interpreted as the pair echo produced by very-high-energy gamma-rays propagating through intergalactic medium with magnetic field of the strength log(B/G)=-16.2+/- 0.7, if its correlation length lambda_B is larger than 20 kpc. If the field correlation length is shorter than 20 kpc, the field strength estimate is modified upwards by a square root of (20 kpc / lambda_B). In the specific case of short correlation length IGMF that is relic from cosmological phase transitions, the pair echo model of the LST-1 signal implies the field strength in the 1e-14-1e-12 G range. Such magnetic field parameters are consistent with all known constraints on IGMF, including the lower bounds from gamma-ray observations of active galactic nuclei.
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All authors Andrii Neronov, Ievgen Vovk, Teneman Keita, Davide Miceli

Cosmology and Nongalactic Astrophysics

Gravitational-wave background from supermassive black holes without merger trees: Tidally regulated mergers and direct inference from the NANOGrav 15 yr data

Shin'ichiro Ando

We present a semi-analytic framework that computes the gravitational-wave background (GWB) from supermassive black hole (SMBH) binaries by direct integration of an $N$-body-recalibrated extended Press-Schechter accretion kernel, bypassing Monte Carlo merger trees entirely. The calculation is resolution-free and fast enough to be sampled directly against pulsar-timing data with no emulator or precomputed model bank. Between halo accretion and black-hole binary formation, we couple the satellite's simulation-calibrated tidal mass loss continuously to Chandrasekhar dynamical friction. Satellites below a sharp, nearly redshift-independent mass-ratio threshold, $\xi \simeq 0.04$, are stripped faster than they sink and stall: their drag collapses onto the stellar core, and 38% of accreted satellites are unmerged by $z=0$. Combining this population model with per-binary stellar-hardening turnovers and eccentric spectra, we sample the five-parameter posterior directly against the NANOGrav 15 yr Hellings-Downs-correlated free spectrum, excluding the $15.8$ nHz bin, whose excess power a subsequent chromatic-noise reanalysis attributes to pulsar noise. The data prefer a black-hole mass normalization $+0.31^{+0.20}_{-0.23}$ dex above the locally calibrated black-hole-bulge mass relation, consistent with earlier indications that the nanohertz background is loud relative to local SMBH calibrations and robust to the delay model, merger kernel, local mass calibration, and its redshift evolution. The spectrum is compatible with, but does not require, eccentric binaries or dense stellar environments.
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Cosmology and Nongalactic Astrophysics

JESSNet: Joint dEconvolution and Sparse Separation Network for HI 21 cm foreground cleaning

Athanasia Gkogkou, Victor Bonjean, Jean-Luc Starck et al. (+3 more)

Foreground cleaning is a major challenge for H\,i 21 cm intensity mapping, particularly in the presence of a chromatic instrumental beam that couples angular foreground structure into the frequency direction and under incomplete sky coverage. We introduce JESSNet, a beam-aware, mask-compatible foreground-cleaning framework for single-dish intensity mapping. Building on SDecGMCA, JESSNet introduces three main extensions: a multiscale angular decomposition with scale-dependent mixing matrices and channel selection, a learned spherical-wavelet ”learnlet” sparse regularization operator, and a mask-constrained reconstruction applicable to Galactic masks and survey footprints. We test JESSNet on simulated SKA-MID-like observations over $900\text{-}1300\,{\rm MHz}$ ($z\simeq0.09\text{-}0.58$), including H\,i emission, Galactic and extragalactic foregrounds, thermal noise, and an oscillating MeerKAT-inspired chromatic beam. The multiscale reconstruction accurately recovers the angular and frequency power spectra of the input H\,i signal, improves the recovery at low and intermediate angular scales relative to a single-scale implementation, and reduces residual beam-induced spectral features. JESSNet also remains effective for a synthetic survey footprint, preserving the H\,i power spectra under incomplete sky coverage. The code and analysis pipeline are publicly released to facilitate reproducibility and future applications to simulated and observational data.
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All authors Athanasia Gkogkou, Victor Bonjean, Jean-Luc Starck, Pauline Gorbatchev, Marta Spinelli, Panagiotis Tsakalides

Cosmology and Nongalactic Astrophysics

Limited Impact of CMB B-mode Polarization on Constraints on Cosmic Topology

Ryota Himeno, Atsushi J. Nishizawa and Kiyotomo Ichiki

The global spatial structure of the universe is a fundamental question in cosmology. Although the standard model usually assumes a trivial topology, a multiply connected universe can break statistical isotropy and generate off-diagonal covariance between the spherical-harmonic coefficients of cosmic microwave background fluctuations. In this work, we investigate whether CMB B-mode polarization improves constraints on the cubic three-torus, or $E_1$ topology. We construct the full harmonic-space covariance matrices of the temperature, E-mode, and primordial B-mode anisotropies, including correlations between different $(\ell,m)$ modes, and evaluate Gaussian likelihoods using random realizations generated from a statistically isotropic $\Lambda$CDM model with trivial topology. To isolate the intrinsic topological information carried by each CMB observable, we consider the ideal cosmic-variance-limited case, neglecting instrumental noise and gravitational lensing. We find that adding primordial B-mode polarization yields only a marginal improvement in the ability to distinguish the $E_1$ topology from the trivial topology, even under these ideal conditions. The different constraining powers of the temperature, E-mode, and B-mode anisotropies can be understood through the combined effects of their transfer-function responses and the topology-induced off-diagonal correlations in harmonic space. }
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Cosmology and Nongalactic Astrophysics

Testing $\Lambda$LTB as an alternative to dynamical dark energy

Yukang Zhang and Pengjie Zhang

A cosmological constant $\Lambda$ in a universe weakly violating the cosmological principle (CP) can mimic a dynamical dark energy (DDE) in a FRW universe, and therefore challenging the recently reported DDE evidences. We test this scenario in the form of $\Lambda$LTB cosmology, against two data combinations. (1) DESI DR2 BAO, Planck CMB, together with any of the four SNe Ia compilations (UNION3, Pantheon+, DES SN5YR, and DES Dovekie) show no preference over DDE or $\Lambda$LTB. (2) The inclusion of the kinematic Sunyaev Zel'dovich (kSZ) effect rules out a large portion of the CP violation parameter space allowed by (1). However, the existence of a $\sim 300$ Mpc$/h$ region with $\sim 10\%$ matter density excess is still allowed by the current data, and therefore remains a viable alternative to DDE. To facilitate further tests, we present analytical expressions of the distance-redshift relation and the kSZ effect in a universe with weak CP violation.
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Cosmology and Nongalactic Astrophysics

Constraints on Nonlinearity of the Mass-Concentration Relation

Nobuhiro Okabe

We develop a Bayesian generalization of the previous method to constrain a wide variety of mass-concentration (M-C) relations motivated by both theoretical and observational studies. The framework incorporates the intrinsic scatter in concentration, nonlinear weak-lensing (WL) calibration relations, the WL measurement-error covariance, and the underlying parent mass distribution. We employ Hamiltonian Monte Carlo for computational efficiency. Our sample consists of 213 X-ray-selected clusters with WL measurements for the eRASS1, XXL, LoCuSS, and MCXC catalogs at 0<z< 0.9. For each subsample, we account for its specific WL calibration relation and underlying population distribution. We consider a conventional single power-law model, an empirical double power-law model, and four theoretical models calibrated against numerical simulations. The four theoretical M-C models comprise two in which concentration decreases with mass, distinguished by the sign of d^2ln c/d(ln M)^2, and two in which the concentration decreases with increasing mass before turning upward at high masses. Because the mass and redshift ranges of our cluster sample do not extend into the upturn regime predicted by numerical simulations, we distinguish among the models primarily through the curvature of their M-C relations. Regardless of which model is adopted, the inferred M-C relation is in good agreement with the results of recent numerical simulations. We find no statistically significant differences among the models above the $4\sigma$ level. However, the result shows a tendency toward a gradual flattening of the mass dependence toward higher masses. Specifically, a monotonically decreasing model with positive curvature is preferred over the single power-law relation and a monotonically decreasing model with negative curvature at the $2\sigma$ level and over three double power-law models at the $0.5-1\sigma$ level.
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